A growing demand for video/data from the Internet and other networks increases the demand for high-speed data transport in transmission and delivery systems, especially at what is known as “the last mile”. Telecommunications operators are deploying a large number of fibre links in order to provide broadband access to the end user based on Passive Optical Networks (PONs). With the increasing number of fibres and cables, the probability of fault at some point of the PON also increases, generating a demand for fibre inspection.
In order to ensure operation that satisfies requirements setup by standards organisations and governments, the specifications relating to monitoring of these deployed networks are generally stricter than traditional supervision or monitoring systems. This is balanced against operational expenses, which requires operators to provide relatively inexpensive solutions to monitor their networks.
For PONs, the technical requirements with respect to e.g. resolution are stricter as compared to traditional monitoring systems based on Optical Time Domain Reflectometry (OTDR) in order to localise faults with reasonable accuracy, and enough dynamic range must be accomplished to monitor split ratios up to 1:128 that could be used in remote nodes located on distances up to 60 km away.
The use of standard OTDRs without auxiliary devices has been ineffective in locating and measuring the fails and/or losses of optical fibres with adequate accuracy.
Prior art technologies have been suggested in order to improve the accuracy of fault localization and loss measurements in fibre links, as well as to increase the dynamic range of the measurement devices. In one of these technologies, a remote amplification system is used which is referred to as an extender box. The extender box can be used for data and monitoring signals. However, a problem with proposed extender boxes is their lack of interaction with commercially available OTDR devices. Generally, commercial OTDR devices are configured with internal software executing complex algorithms to improve their dynamic range. For example, these algorithms commonly perform subtraction of the background signal to characterize the optical fibre to be monitored. However, if continuous light is spread from the extender box through the fibre link, as it is the case for amplified spontaneous emission (ASE) signals appearing in optical amplifiers comprised in the extender box, software failure may occur causing measurement errors or even aborted measurement and, in some cases, permanent damage to the OTDR device.